This invention relates to a process and product for developing blueprints, wherein the developed blueprint does not exhibit the characteristic, unpleasant smell of ammonia.
The process for producing blueprints is well known. The desired image is produced on a translucent paper, and this paper is placed over a light sensitive blueprint paper and exposed to ultraviolet light. The blueprint paper is then treated with a developing chemical in the form of a strong base, generally ammonia. The ammonia activates dyes in the unexposed areas of the paper that produce a blue or other color image (depending on the color of the dye used) on the paper.
The active chemicals in blueprint paper are diazo compounds. These are light sensitive compounds that decompose and produce no image (white) when exposed to ultraviolet light. Blueprint paper is impregnated with both diazo compounds and a composition called a coupler, which couples with diazo compounds to produce azo dyes. In blueprint paper, the diazo compounds and coupler are in the presence of a stablizing acid barrier, which prevents premature coupling. Blueprints are developed by exposing the paper to a strong base that neutralizes the acid. This permits coupling and causes the release of azo dyes in unexposed areas lying under the image to be reproduced.
Ammonia is a gas at room temperature but can be liquefied under pressure or can be placed in solution with a suitable liquid such as water. Ammonia is used in blueprint developing machines in both forms. Ammonia vapor, either provided directly from liquid ammonia or by vaporization from a water solution of ammonia, permeates the blueprint paper and activates the dyes in the paper. This typically occurs in an enclosed developing chamber in a blueprint developing machine at an elevated temperature of about 170.degree.-210.degree. F., depending on the system. When the blueprint paper is removed from the developing chamber, the blueprint image is on the paper, but the paper also retains a certain amount of ammonia in the fibers of the paper. This gives the blueprint copies an unpleasant odor characteristic of ammonia.
It is desirable that a developing solution of ammonia (whether it be liquid ammonia or an ammonia-water solution) retain its characteristic odor of ammonia, because such a solution produces highly concentrated ammonia fumes that are very toxic at the concentration levels found in a blueprint developing solution. The characteristic odor of ammonia is an important safeguard for persons using this material.
On the other hand, the level of ammonia in a developed blueprint is of such a low level that toxicity is no concern and the odor is merely an annoyance.
A number of attempts have been made to reduce or eliminate the odor of blueprints, but none to date have been adequately successful.
One purpose of the present invention is to provide a means for eliminating the odor of ammonia from developed blueprints without eliminating the warning odor provided by ammonia in a developing solution itself.